The present invention capitalizes on the advantages inherent in recording images on an intermediate member and then transferring those images to a recording sheet or substrate. One primary advantage of such a system is the increased ability to control the critical spacing parameters in the transfer gap between the marking and/or development devices and the intermediate member. As is the case with most marking technologies, the characteristic variations inherent in the recording sheets requires the marking mechanisms to be developed with wide latitudes to accommodate such variations.
Heretofore, various marking methods have employed an intermediate member or have combined transfer-fixing (transfix) steps in the marking process, some being the subject of the following disclosures which may be relevant:
U.S. Pat. No. 3,013,878 Patentee: Dessauer Issued: Dec. 19, 1961 PA1 U.S. Pat. No. 3,374,769 Patentee: Carlson Issued: Mar. 26, 1968 PA1 U.S. Pat. No. 3,591,276 Patentee: Byrne Issued: Jul. 6, 1971 PA1 U.S. Pat. No. 3,794,418 Patentee: Makino et al. Issued: Feb. 26, 1974 PA1 U.S. Pat. No. 3,848,204 Patentee: Draugelis et al. Issued: Nov. 12, 1974 PA1 U.S. Pat. No. 4,195,927 Patentee: Fotland et al. Issued: Apr. 1, 1980 PA1 U.S. Pat. No. 4,267,556 Patentee: Fotland et al. Issued: May 12, 1981 PA1 U.S. Pat. No. 4,365,549 Patentee: Forland et al. Issued: Dec. 28, 1982 PA1 U.S. Pat. No. 4,373,799 Patentee: Snelling et al. Issued: Feb. 15, 1983 PA1 U.S. Pat. No. 4,427,285 Patentee: Stange Issued: Jan. 24, 1984 PA1 U.S. Pat. No. 4,448,872 Patentee: Vandervalk Issued: May 15, 1984 PA1 U.S. Pat. No. 4,518,468 Patentee: Fotland et al. Issued: May 21, 1985 PA1 U.S. Pat. No. 4,935,785 Patentee: Wildi et al. Issued: Jun. 19, 1990 PA1 U.S. Pat. No. 5,087,946 Patentee: Dalai et al. Issued: Feb. 11, 1992 PA1 U.S. Pat. No. 5,168,289 Patentee: Katakabe et al. Issued: Dec. 1, 1992 PA1 U.S. Pat. No. 5,175,568 Patentee: Oyamaguchi et al Issued: Dec. 29, 1992 PA1 Tacky Toner Transfer Method Xerox Disclosure Journal R. C. Vock Vol. 3, No. 4, p. 273 (July/August 1978) PA1 Thermal Ink Jet Printing in an Indirect Marking System Xerox Disclosure Journal Bruce J. Parks et al. Vol. 16, No. 6, pp. 349-350 (November/December 1991)
The relevant portions of the foregoing patents are hereby incorporated by reference, and may be briefly summarized as follows:
U.S. Pat. No. 3,013,878 to Dessauer discloses an improved method and apparatus for transferring and fixing a xerographic powder image on a support. Specifically, the patent discloses an electrostatic latent image formed on a sheet of insulating material in surface contact with a xerographic plate to form a reverse reading latent image thereon. The electrostatic latent image on the material is then developed to form a reverse reading powder image. While the xerographic powder image is adhered to the insulating material it is "tackified", meaning that the individual powder particles are softened so that they coalesce, becoming sticky, but not extending beyond the boundary of the developed latent image pattern. While in the tackified condition, the final support material is superposed on the tackified image and then uniformly pressed into intimate surface contact therewith, so that the application of pressure causes the tackified powder material to flow into the interstices of the support material and bond therewith. Moreover, relatively little bonding occurs between the tackified powder and the surface of the insulating material. A similar process is disclosed by Vock in the Xerox Disclosure Journal, Vol. 3, No. 4, p. 273 (July/August 1978).
U.S. Pat. No. 3,374,769 to Carlson teaches an apparatus employing an intermediate belt to which is transferred a developed image, where it is subsequently heated to tackify the transferred image and then transferred to a sheet of paper. The intermediate belt is transparent, allowing heat to be applied, by reflectance, to both sides of the powder image previously transferred thereto.
U.S. Pat. No. 3,591,276 to Byrne describes a method and apparatus employing an elastomeric intermediate transfer member After developing a latent electrostatic image using conventional methods, the image is transferred to the elastomeric member under pressure to capture the developed powder image. Subsequently, the image is re-transferred to a paper support material by heat and pressure. Moreover, the patent discloses that the paper support material may be preheated, or alternatively heat may be applied at the contact transfer nip, to facilitate re-transfer of the image to the support material.
U.S. Pat. No. 3,794,418 to Makino et al. teaches an imaging system employing an insulating web. More specifically, the insulating web is charged to opposite polarities on either side thereof, with one side being brought into contact with a photoconductive layer, while simultaneously exposing the photoconductive layer to a light-and-shadow image. Subsequently, the electrostatic image formed by this process is developed by application of toner particles, or the electrostatic image may be subsequently transferred to another member before development.
U.S. Pat. No. 3,848,204 to Draugelis et al describes an apparatus in which a developed image of electrostatically charged particles is transferred from an image bearing member to a sheet of support material, while a substantially constant potential difference is maintained between the image bearing member and a sheet support means. The potential difference attracts the developed particles to the sheet of support material secured to the support means.
U.S. Pat. No. 4,195,927 to Fotland et al. discloses an electrophotographic system employing double image transfer. Here, a photoconductive member is charged and exposed to form a latent electrostatic image, which is then transferred to a drum with a durable dielectric coating. The latent electrostatic image is subsequently developed and transferred by pressure to a recording medium with or without simultaneous pressure fixing.
U.S. Pat. No. 4,267,556 to Fotland et al. describes the process of electrostatic transfer printing utilizing an ion emitting print head, where an image is formed on a cylindrical dielectric member by means of an ion source. Subsequently, the image is toned and pressure-transferred to a sheet of paper which is passed between the cylindrical dielectric member and a transfer roller. The patent further describes the possible use of a mesh screen adjacent to the dielectric cylinder to neutralize residual charge remaining on the surface thereof. U.S. Pat. No. 4,365,549 to Fotland et al., a continuation of the previously described patent, further discloses the characteristics of the ion generating means, a multiplexed matrix of control and driver electrodes, as well as, the potential use of a scraper blade to clean the surface of the dielectric member subsequent to image transfer. Specifics of the dielectric surface employed by the Fotland et al. patents can be found in U.S. Pat. No. 4,518,468.
U.S. Pat. No. 4,373,799 to Snelling et al. discloses a multi-mode printing machine capable of printing electrophotographically or electrographically. In either, or both modes, electrostatic charge is transferred to a dielectric sheet which is subsequently developed to form an image thereon. In the electrographic mode, a sheet width stylus array is used to selectively transfer ions to the surface of the dielectric sheet.
U.S. Pat. No. 4,427,285 to Stange teaches a direct duplex printing apparatus which utilizes a pair of pre-fuser transport rolls to "tack" unfused images to a copy sheet. The fuser comprises a pair of heated soft fuser rolls, operating at slightly lower temperature due to the tacking achieved by the pre-fuser treatment.
U.S. Pat. No. 4,448,872 to Vandervatk describes a duplex electrographic imaging method and apparatus utilizing simultaneous transfixing of toner images to opposite sides of a receptor medium using high pressure alone. After developing a latent electrostatic image on an image roll, the image may be transferred, by direct contact, to a transfer roll. Subsequently, a second image may be developed on the image roll. Upon passing a receptor sheet between the two rolls, the image from the imaging roll is transferred to a first surface thereof, while the image previously transferred to the transfer roll is transferred to the opposite surface thereof.
U.S. Pat. No. 4,935,785 to Wildi et al. discloses a fuser roll having a surface of an electric material, where, n the surface of the fuser roll may be charged to the same polarity as that of the toner being fused, thereby avoiding the need for fuser oils.
U.S. Pat. No. 5,087,946 to Dalai et al. describes a fuser roll including a hollow cylinder having a relatively thin wall, wherein the wall is formed of a plastic composition with a conductive fiber filler. The conductive fiber filler forms a heating element within the thin wall of the fuser roll, as well as providing mechanical reinforcement thereto. Hence, the mass of the fuser roll is reduced, requiring less energy and resulting in an "instant-on" fuser.
U.S. Pat. No. 5,168,289 to Katakabe et al. discloses a recording apparatus that employs an ink sheet, coated with a thermoplastic ink, to selectively deposit an image onto an intermediate transfer drum. The intermediate transfer drum is then advanced so as to bring the thermoplastic ink, which was deposited on a silicon elastomer layer on the surface of the drum, into contact with recording paper. The patent further describes the transfer to the recording paper as being achieved while the ink remains above its melting point. As described beginning at col. 7, line 28, a halogen lamp is used to radiate the intermediate transfer surface just prior to contact with the recording paper. Multicolor images are formed on the intermediate transfer drum in a superimposed manner while the halogen lamp remains off, and are then transferred to the recording sheet by turning the lamp on in the presence of the recording sheet to effect transfer thereto.
U.S. Pat. No. 5,175,568 to Oyamaguchi et al. teaches an image forming process which utilizes a recording medium having the characteristic of a decrease in the receding contact angle when heated. Utilizing this characteristic the image forming process may be described with respect to FIG. 8 (see col. 18 line 22 through column 19, line 4). Briefly, the recording medium is selectively heated so that the heated areas attract a solid ink which has been heated above its melting temperature, thus "developing" the heated regions only. The solid ink image is then transferred to a recording sheet while the ink is still soft, to form a visible image thereon. After transfer, the latent image remaining on the recording medium is erased by heating the recording medium with an infrared lamp.
In the Xerox Disclosure Journal publication by Parks et al. (Vol. 16, No. 6, pp. 349-350 (November/December 1991)), the use of a thermal ink jet marking head is disclosed whereby the ink image is first deposited on an intermediate transfer drum or similar media. Subsequently, the ink image is transferred to a copy sheet.
In accordance with the present invention, there is provided a recording apparatus for producing an image on a recording sheet. The apparatus comprises an intermediate member, marking means for depositing marking material on an outer surface of said intermediate member to form an image thereon, a heater, in communication with an internal surface of said intermediate member, for heating said intermediate member so as to cause the tackification of the charged marking material deposited on the outer surface thereof, and means, defining a nip with the outer surface of said intermediate member, for transferring the tackified marking material image to the recording sheet passing through the nip defined by said intermediate member and said transferring means, whereby the tackified marking material image is cooled upon contact with the recording sheet to become permanently fixed to the surface of the recording sheet.
In accordance with another aspect of the present invention, there is provided a duplex recording apparatus for producing images on both sides of a recording sheet. The apparatus comprises first and second imaging systems. Each imaging system including an intermediate member, marking means for depositing marking material on an outer surface of the intermediate member to form an image thereon, and a heater, in communication with an internal surface of said intermediate member, for heating said intermediate member so as to cause a coalescence and tackification of the charged marking material deposited on the outer surface thereof. The apparatus further comprises means, defining a nip between the first and second intermediate members, for forcing said first and second intermediate members into contact with the respective sides of a recording sheet passing through the nip, so as to transfer the tackified marking material images on said first and second intermediate members to the respective sides of the recording sheet, thereby permanently fixing the tackified images thereto.
In accordance with yet another aspect of the present invention, there is provided a method for producing an image on a recording sheet, comprising the steps of: a) non-interactively generating a developed image of charged marking particles on an outer surface of an intermediate member; b) heating at least a portion of the interior of said intermediate member so as to cause the tackification of the marking particles; and c) contacting the outer surface of said intermediate member with the recording sheet to transfer the tackified marking material to the recording sheet.
The present invention has the advantage of a fixed image forming gap, where the latent and/or developed images are produced on the intermediate member, which enables the printing device to be specifically tailored without having to allow for a wide range of recording media that pass through the gap in common electrostatic printing machines. A further advantage of the present invention is that the heat applied to the endless intermediate member is used to heat only the marking particles contained on the surface of the member. This avoids the need for additional energy to heat the recording sheet passing through the transfer nip, and/or subsequent fusing of the marking material transferred to the recording sheet to achieve complete fixing to the sheet. Yet another advantage of the present invention is the elimination of electrostatic fields as the method of transferring the marking particles to the surface of the recording sheet. Not only does this eliminate an energy intensive corona element, but it also improves the reliability with which the marking particles can be transferred to textured or wrinkled recording sheets, for example, recording sheets being subjected to multiple pass duplex imaging.